Method for cast coating paper



United States Patent Ofilice 3,ll3,88? Patented Dec. it), 1963 3,113,887 METHOD FOR CAST COATENG PAPER Joseph R. Wiehush, Silver Spring, Md, assignor to The llead Corporation, Dayton, Ohio, a corporation of hit) N Drawing. Filed Apr. 28, 1959, Ser. No. 809,352 14 Claims. (Cl. 1117-64) This invention relates to a process for the production of high gloss cast surfaced mineral coated papers, and more particularly to agents effective in providing ready and complete release of such coated papers from a casting surface.

In the manufacture of cast surfaced mineral coated papers, a paper Web carrying a wet, plastic mineral coating composition is pressed into adherent contact with a highly polished casting surface, such as a chromium plated drum or belt, and dried thereon. Thereafter, the dried coated paper is intended to separate from the casting surface with a surface gloss or finish which approaches the gloss of the casting surface.

A difficulty often encountered in the production of cast surfaced mineral coated paper is sticking of the dried and set coating to the casting surface, resulting in marring 0f the coated paper surface by particles of the dried coating which adhere to the casting surface. This sticking may become so extreme that the entire area of the paper in contact with the casting surface becomes tightly bonded thereto and is only removed by long and laborious treatment. Obviously, such a sticking condition makes the process of cast coating inoperable.

To overcome this sticking tendency, various means have been proposed in the prior art. Most such proposals make use of materials which are described as release agents, and such agents are applied directly to the casting surface by rubbing or polishing means, or are applied indirectly by incorporation of the release agent in the coating composition or by contacting the coating and/0r casting surface with a solution or dispersion of the release agent.

Release agents which have been used in the prior art are soaps, oils, fats, certain alkali-soluble natural and synthetic resins, and other synthetics such as dimers of aliphatic ketenes. None of the prior materials is completely satisfactory. While serving to effect release of the dried coating from the casting surface under critical conditions, the prior art release agents fail in one or more respects. Thus, soaps are prone to cause foam when used in the coating composition and yield cast coated paper products which are unduly sensitive to moisture. Oils and fats have a limited operating tolerance, in that a slight change in quantity causes either a sticking condition on the casting surface when the quantity is inadequate, or a loss of gloss in the cast coated paper product when the quantity is too abundant. Such materials also undergo at least partial saponification when used in the normally alkaline cast coating compositions, and suffer to some degree from the shortcomings of the soaps, as aforementioned. Alkali soluble resins may cause undesirable effects on viscosity or stability of the coating composition, and result in undesirable properties of the finished cast coated paper, such as reduced ink adsorption, extreme water repellency, or the like. Other materials, such as the ketene dimers, require an emulsification step before they can be used.

These and other shortcomings of the prior art release agents have been unexpectedly overcome by the release agents of this invention. Furthermore, the release agents of this invention provide an important additional feature in the reduction or substantial elimination of static electricity in the cast coated paper product.

Accordingly, it is a principal object of this invention to provide new and useful release agents for the manufacture of cast coated paper.

A further object is the provision of such release agents which permit a wide operating tolerance.

Still another object is to provide such release agents which are adaptable to high speed cast coating operations.

An additional object is to provide such release agents which are effective over a wide range of concentration.

Numerous other objects and advantages of the invention will be apparent from the following description and the appended claims.

The preferred release agents of this invention are alkyl phosphate materials which are mixture of monoand dialkyl orthophosphates; and the alkanol amine salts thereof. The mixture of mono and dialkyl orthophosphate may suitably contain from 10 to 50 mole percent of the diester. The alkyl radical is suitably a straight-chained, saturated, aliphatic normal hydrocarbon radical of from 8 to 16 carbon atoms. The alkanol amine used to form the amine salts of the monoand dialkyl orthophosphate is suitably diethanolamine. Chemically, the preferred alkyl phosphate materials of this invention mav he. rem resented by the general formula in which Alk is a normal alkyl radical having from 8 to 16 carbon atoms. Such materials may be prepared by reacting one mole of phosphorous pentoxide with about three moles of the desired alcohol. If desired, the product may be further reacted with three moles of diethanolamine. A particularly suitable alkyl phosphate material is obtained when the alcohol used is a mixture of 1 mole of n-octanol-l, 1 mole of n-decanol-l, and 1 molecular equivalent of Lorol (a commercial mixture of primmy alcohols, predominantly C and C The alkyl phosphate materials of this invention range from a fluid to a pasty character at room temperature, becoming more fluid at elevated temperatures. They are readily dispersible in aqueous coating compositions and are conveniently stirred into such a composition of the pigment-adhesive type normally used in making cast coated papers. More specifically, the alkyl phosphate materials of this invention are readily dispersed in the coating compositions disclosed in the color formula examples of the hereinafter referred to copending Smith application, infra. Quite unexpectedly, such alkyl phosphate materials, when present as a relatively thin layer on a casting surface, provide complete and ready release of dried coatings which have been dried in contact therewith.

Without limiting this invention, the following examples are given by way of illustration.

Example I A polished chromium plated, internally heated casting drum was thoroughly cleaned, rinsed with water and wiped dry with a soft cloth. Thereafter, a thin layer of an equimolecular mixture of monoand dialkyl orthophosphate, in which the alkyl radicals were derived from mixed normal alcohols having 8, l0, l2 and 14 carbon atoms in the chain, was applied to the chromium surface by rubbing with a soft cloth. The casting surface so prepared was then used for making cast surfaced mineral coated paper according to the process disclosed in copending Smith application Serial No. 648,227, filed March 25, 1957, now U.S. Patent 2,950,214, and assigned to the assignee of this invention. The dried. cast coated paper separated freely and completely from the casting surface, and had a gloss closely approaching the gloss of the polished chromium surface. It was further observed that the dried cast coated paper was substantially free of p a static electricity, although such static is generally evident under similar conditions, in the absence of the alkyl phosphate material.

Example 2 Example 3 Cast surfaced mineral coated paper was made according to the process disclosed in the Smith application supra, with the addition of varying amounts of the alkyl phos phate material of Example 1 to the aqueous coating composition, which comprised adhesive and mineral pigment. It was found that release of the dried cast coated paper from the casting surface was readily and completely accomplished when the amount of alkyl phosphate material in the coating composition ranged from 0.25% to 2.0%, based on the solids content of the coating composition. Included in these casting operations were coating compositions containing 0.25, 0.5, 1.0, 1.5 and 2.0% respectively of the alkyl phosphate material. In each case, the cast coated paper was found to have a gloss closely approaching that of the polished chromium casting surface, and, in each case, the cast coated paper was substantially free of static electricity. In this example, the thin releasing layer of alkyl phosphate material on the chromium casting surface was established and maintained by transfer or adsorption of alkyl phosphate material from the Wet coating composition during its contact with the casting surface.

Example 4 A thin layer of the alkyl phosphate material of Example 1 was rubbed directly on the previously cleaned and dried casting surface, thereafter, the procedures of Example 3 were followed to make substantially static-free, highly glossed mineral coated paper which, after drying, separated freely from the casting surface.

Example 5 The procedure was that of Example 3, using the alkyl phosphate material of Example 2. The product was substantially static-free, highly glossed cast coated paper which exhibited no tendency to stick to the casting surface after drying thereon.

Example 6 The procedure was that of Example 4 using the alkyl phosphate material of Example 2. Here again, there was no tendency for the dried cast coated paper to stick to the casting surface. The paper so produced had a gloss closely approaching that of the polished chromium casting surface, and was substantially free of static electric charges.

In addition to the unexpected release properties of the alkyl phosphate materials of this invention, it has also been found that these materials provide substantially complete static electricity elimination. Static electricity has long been a particular annoyance to makers and users of paper, and its substantial elimination is a highly desired accomplishment.

While the products and methods herein described are for purposes of illustration only, it is to be understood that the present invention includes all modifications and equivalents which fall within the scope of the invention which is defined by the appended claims.

What is claimed is:

1. In a process for making cast surfaced mineral coated paper which utilizes a release agent to insure separation of the dried coating from a casting surface, the improvement which comprises applying on said casting surface a thin releasing layer of alkyl phosphate material selected from mixed monoand dialkyl orthophosphates and diethanolamine salts thereof, the alkyl groups of said mixed phosphates having from 8 to 16 carbon atoms in the chain and said material having an equimolecular ratio of monoto dialkyl orthophosphates.

2. The process according to claim 1 in which the thin releasing layer of alkyl phosphate material is applied directly to the casting surface.

3. The process of claim 2 in which the alkyl phosphate material comprises an equimolecular mixture of monoand di-alkyl orthophosphate wherein the alkyl radical is a straight chained, saturated aliphatic primary hydrocarbon radical of from 8 to 16 carbon atoms.

4. The process of claim 2 in which the alkyl phosphate material comprises an equimolecular mixture of monoalkyl bis (diethanolamine)-orthophosphate and dialkylrnono (diethanolamine)-orthophosphate wherein the alkyl radical is a straight-chained, saturated, aliphatic primary hydrocarbon radical of from 8 to 16 carbon atoms.

5. The process according to claim 1 in which the thin releasing layer is applied to the casting surface by adsorp- 'tion of alkyl phosphate material contained in the coating composition.

6. The process of claim 5 in which the alkyl phosphate material comprises an equimolecular mixture of mono- :and dialkyl orthophosphate wherein the alkyl radical is a straight-chained, saturated aliphatic primary hydrocarbon radical of from 8 to 16 carbon atoms.

7. The process of claim 5 in which the alkyl phosphate material comprises an equimolecular ratio of monoalkyl bis (diethanolamine)-orthophosphate and dialkyl-mono (diethanolarnine) orthophosphate wherein the alkyl radical is a straight-chained, saturated aliphatic primary hydrocarbon of from 8 to 16 carbon atoms.

8. The process of claim 5 in which the alkyl phosphate material is present in the coating composition to the extent of from 0.25-20% of the solids content thereof.

9. In a process for making cast surfaced mineral coated paper which utilizes a release agent to insure separation of the dried coating from a casting surface, the improvement which comprises maintaining on said casting surface a thin releasing layer of alkyl phosphate material selected from mixed monoand dialkyl orthophosphates and diethanolamine salts thereof, the alkyl groups of said mixed phosphates having from 8 to 16 carbon atoms in the chain and said material having an equimolecular ratio of monoto dialkyl orthophosphates.

10. In a process for making cast surfaced mineral coated paper wherein an aqueous coating composition comprising adhesive and mineral pigment is applied to a paper web and gelled by contact with an aqueous electrolyte solution prior to its application into adherent contact with a heated polished casting surface from which it releases after substantial drying thereon, the improvement which comprises applying to the polished casting surface a releasing layer of a mixture of monoand dialkyl orthophosphates and incorporating in the coating composition from 0.25 to 2.0%, based on solids content, of the said phosphate mixture, the alkyl groups of said monoand dialkyl orthophosphate having from 8 to 16 carbon atoms in the chain, and said mixture having an equimolecular ratio of monoto dialkyl orthophosphate.

11. In a process of making cast surfaced mineral coated paper wherein an aqueous coating composition comprising adhesive and mineral pigment is applied to a paper web and gelled by contact with an aqueous electrolyte solution prior to its application into adherent contact with a heated polished casting surface from which it releases after substantial drying thereon, the improvement which comprises incorporating in the coating composition from 0.25 to 2.0% of a mixture of monoand dialkyl orthophosphates wherein the alkyl radical of said mixed phosphates is a straight-chained saturated aliphatic normal hydrocarbon of from 8 to 16 carbon atoms, said mixed phosphates having an equimolecular ratio of monoto dialkyl orthophosphate.

12. In a process for making cast surfaced mineral coated paper wherein an aqueous coating composition comprising adhesive and mineral pigment is applied to a paper web and gelled by contact With an aqueous electrolyte solution prior to its application to adherent contact with a heated polished casting surface from which it releases after substantial drying thereon, the improvement which comprises applying to the polished casting surface a releasing layer of a mixture of monoand dialkyl orthophosphates, the alkyl groups of which contain from 8 to 16 carbon atoms in the chain, said mixed phosphates having an equimolecular ratio of monoto d-ialkyl phosphate.

13. In a process for making cast surfaced mineral coated paper which utilizes a release agent to insure separation of the dried coating from a casting surface, the improvement which comprises applying on said casting surface a thin releasing layer of alkyl phosphate material selected from mixed monoand dialkyl orthophosphates and diethanolamine salts thereof, the alkyl groups of said mixed phosphates having from 8 to 16 carbon atoms in the chain.

14. In a process for making cast surfaced mineral coated paper which utilizes a release agent to insure separation of the dried coating from a casting surface, the improvement which comprises applying on said casting surface a thin releasing layer of alkyl phosphate material selected from mixed monoand dialkyl orthophosphates and diethanolamine salts thereof, the alkyl groups of said mixed phosphates having from 8 to 16 carbon atoms in the chain and said material having from 10 to mole percent of the dialkyl orthophosphates.

References Cited in the file of this patent UNITED STATES PATENTS 2,193,965 Hochwalt Mar. 19, 1940 2,285,854 Downing et a1. June 9, 1942 2,360,825 Blickensderfer Oct. 24, 1944 2,397,381 Smith et a1. Mar. 26, 1946 2,568,288 Montgomery Sept. 18, 1951 2,676,122 McCarthy Apr. 20, 1954 2,676,924 Fortess et a1 Apr. 27, 1954 2,819,184 Smith et al. Jan. 7, 1958 2,853,451 Fortess et al Sept. 23, 1958 

1. IN A PROCESS FOR MAKING CAST SURFACED MINERAL COATED PAPER WHICH UTILIZES A RELEASE AGENT TO INSURE SEPARATION OF THE DRIED COATING FROM A CASTING SURFACE, THE IMPROVEMENT WHICH COMPRISES APPLYING ON SAID CASTING SURFACE A THIN RELEASING LAYER OF ALKYL PHOSPHATE MATERIAL SELECTED FROM MIXED MONO- AND DIALKYL ORTHOPHOSPHATES AND DIETHANOLAMINE SALTS THEREOF, THE ALKYL GROUPS OF SAID MIXED PHOSPHATES HAVING FROM 8 TO 16 CARBON ATOMS IN THE CHAIN AND SAID MATERIAL HAVING AN EQUIMOLECULAR RATIO OF MONOTO DIALKYL ORTHOPHOSPHATES. 